X-51 Waverider makes historic hypersonic flight

Published May 26, 2010
By Air Force Flight Test Center Public Affairs

EDWARDS AIR FORCE BASE, Calif. -- An X-51A Waverider flight test vehicle successfully made the longest ever supersonic combustion ramjet-powered hypersonic flight May 26 off the southern California Pacific coast.

The more than 200 second burn by the X-51's Pratt & Whitney Rocketdyne-built air breathing scramjet engine accelerated the vehicle to Mach 5. The previous longest scramjet burn in a flight test was 12 seconds in a NASA X-43.

The X-51 launched about 10 a.m. Wednesday from Edwards Air Force Base, carried aloft under the left wing of an Air Force Flight Test Center B-52 Stratofortress. Then, flying at 50,000 feet over the Pacific Ocean Point Mugu Naval Air Warfare Center Sea Range, it was released. Four seconds later an Army Tactical Missile solid rocket booster accelerated the X-51 to about Mach 4.8 before it and a connecting interstage were jettisoned. The launch and separation were normal, said Charlie Brink, X-51A program manager with the Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio.

Then the X-51's SJY61 engine ignited, initially on a mix of ethylene, similar to lighter fluid, and JP-7 jet fuel then exclusively on JP-7 jet fuel, the same fuel once carried by the SR-71 Blackbird before its retirement. The flight reached an altitude of about 70,000 feet and a peak speed of Mach 5.

"We are ecstatic to have accomplished most of our test points on the X-51A's very first hypersonic mission," Mr. Brink said. "We equate this leap in engine technology as equivalent to the post-World War II jump from propeller-driven aircraft to jet engines."

Even before sifting through volumes of telemetry data transmitted by the X-51, Air Force officials called the test, the first of four planned, an unqualified success. The flight is considered the first use of a practical hydrocarbon fueled scramjet in flight.

"Onboard sensors transmitted data to an airborne U.S. Navy P-3, as well was ground systems at Point Mugu and Vandenberg and Edwards Air Force Bases," Mr. Brink said. "After about 200 seconds of engine operation a vehicle anomaly occurred and the flight was terminated. Engineers are busily examining the data to identify the cause of the problem. However, because of the overwhelming success of the test, this will be one of the key points to examine in the analysis of several months' worth of data derived from today's flight."

A NASA Dryden Research Center F-18 Hornet flying photo and safety chase captured the X-51A's release from the B-52 on video before it shot out of sight in a blast of smoke from the solid rocket booster motor.

Four X-51A cruisers have been built for the Air Force and Defense Advanced Research Projects Agency by industry partners Pratt & Whitney Rocketdyne and Boeing. The Air Force intends to fly the three remaining X-51A flight test vehicles this fall, Mr. Brink said. The Air Force currently plans to fly each on virtually identical flight profiles, building knowledge from each successive flight.

Mr. Brink said the heart of this aircraft is its SJY61Pratt & Whitney Rocketdyne scramjet engine, which is capable of producing between 400 and 1000 pounds of thrust. Like a conventional jet engine, the SJY61 is capable of adjusting thrust throughout the X-51's flight envelope.

Hypersonic flight, normally defined as beginning at Mach 5, five times speed of sound, presents unique technical challenges with heat and pressure, which make conventional turbine engines impractical. Program officials said producing thrust with a scramjet has been compared to lighting a match in a hurricane and keeping it burning.

George Thum, Pratt & Whitney Rocketdyne X-51 program manager, said the key technical challenge for X-51 has been integrating a fuel-cooled scramjet, where the JP-7 fuel runs through the walls of the engine, cooling it in flight, into a compact flight vehicle capable of hypersonic flight. The X-51's fuel-cooled engine design serves to both heat the JP-7 to an optimum combustion temperature and help the engine itself endure extremely high operating temperatures during the long burn.

Boeing's Phantom Works in Palmdale, Calif., oversaw vehicle systems integration and assembly. Beyond scalable scramjet propulsion, other key technologies the X-51A will demonstrate include thermal protection systems materials, airframe and engine integration, and high-speed stability and control, said Joe Vogel, Boeing's X-51A program manager.

"This first flight was the culmination of a six-year effort by a small -- but very talented -- AFRL, DARPA and industry development team," Mr. Brink said. "Now we will go back and really scrutinize our data. No test is perfect, and I'm sure we will find anomalies that we will need to address before the next flight. But anyone will tell you that we learn just as much, if not more, when we encounter a glitch."

The launch of the X-51A took from 50,000 feet, near the limits of the B-52's capabilities, said project pilot Lt. Col. Daniel Millman.

"Seeing the X-51 come off the rail and streak away was immensely satisfying," Colonel Millman said.

More than 35 people inside the control room at Ridley Mission Control Center at Edwards AFB monitored the X-51A's engine performance and various telemetry. Among them was Johnny Armstrong, a senior technical advisor with the Air Force Flight Test Center's Hypersonics Combined Test Force. Mr. Armstrong began his Air Force career some 50 years ago with another test article carried by the B-52: the rocket-powered X-15.

Mr. Armstrong said it's been a long wait seeing the first proof of concept in a practical, reusable, air-breathing hypersonic scramjet, but he's found the journey very satisfying.

"As we've often said in the flight test community, there will be no test before its time. This one was most definitely worth waiting for," he said.

Program officials said the scramjet motor's great advantage is the ability to capture and burn oxygen in the thin atmosphere, rather than having to carry it in a large tank like the space shuttle or other rockets. Not having to carry the oxidizer needed for combustion means more payload capability.

Mr. Brink noted while development of the X-51A's engine and the test program are complex, controlling costs has been a key objective, and the team has incorporated or adapted existing proven technologies, and elected from the outset not to build recovery systems in the flight test vehicles, in an effort to control costs and focus funding on the vehicle's fuel-coold scramjet engine.

Mr. Brink said he believes the X-51A program will provide knowledge required to develop the game changing technologies needed for future access to space and hypersonic weapon applications.